Ok... I know what this is all about... though I don't know why portage didn't just come out and say it.

It needs libav installed to provide missing libraries.

-However-

These libraries conflict with ffmpeg -- something I really need to have on my system. I have read the portage docs on blocked packages, but I don' really see how I can install both libav and ffmpeg. They basically tell you (using postfix and ssmtp) to choose between one or the other. I can't really do that, here, I need both.